28 THE PRINCIPLES OP AGRICULTURE 



probable effect of this extra food upon the crop, 

 and the commercial value of the extra crop. In 

 general, it should be considered that in mixed 

 husbandry the fertility of the land must be 

 maintained by means of farm -practice (that is, 

 by good farming), and that plant-food should 

 be bought only for the purpose of producing the 

 extra product. 



48. We are now able to comprehend that 

 the soil is a compound of numberless inorganic 

 and organic materials, a realm of complex 

 physical and chemical forces, and the scene of 

 an intricate round of life. We must no longer 

 think of it as mere dirt. Moreover, we are only 

 beginning to understand it; and if the very soil 

 is unknown to us, how complicated must be the 

 great structure of agriculture which is reared 

 upon it ! 



SUGGESTIONS ON CHAPTER I 



25a. The word organic refers to animals and plants or their 

 products and remains ; that is, to things which live and have 

 organs. Organic compounds, in chemistry, are those which 

 have been built up or produced by the action of a plant or 

 animal. Modern usage, however, defines organic compounds as 

 those which contain carbon. Starch, sugar, woody fiber, are 

 examples. 



256. Inorganic compounds are such as are not produced by 

 living organisms, as all the mineral compounds. They are 

 found in the earth and air. Salt, potash, iron and gold, 

 lime, are examples. 



